It has been a common practice to mount a headrest to an automobile seat for the purpose of promoting safety and protecting a passenger in case of an accident such as a collision. To be adjustable to an arbitrary vertical position according to a physical constitution or preference of the passenger, the headrest is provided with a height adjusting mechanism. In general, two headrest stays are firmly fixed to the headrest and supported by being inserted respectively in two headrest bushes that are securely installed on the side of a seat back, and while one of the headrest bushes is provided with the height adjusting mechanism, the other headrest bush is free.
In the case of a collision (including a rear-end collision), the automobile headrest prevents the head of a passenger in the seat from being tilted backwards too much due to an impact of the collision. At this moment, an impact force applied to the head of the passenger acts as a load pressing the headrest downwards. Therefore, the height adjusting mechanism of the automobile headrest allows the headrest to move upwards upon application of an extracting force thereto and to stop at an arbitrary height, and locks the headrest to prohibit it from moving downwards unless an unlocking operation is performed (e.g., see JP-HE1 4-193109 A).
More specifically, headrest stays of the headrest are vertically adjustably inserted and supported in headrest bushes that are securely installed on the side of a seat back. Lock members reciprocating due to a resilient force are attached to the headrest bushes at a position corresponding to an upper end portion of the seat back and abut on the headrest stays respectively. The headrest stays have a plurality of height adjusting notches arranged at a predetermined spacings. The headrest is held at a predetermined height through engagement of the lock members with the notches. In this state, the height adjusting notches are so shaped as to allow the headrest stays to move upwards in relation to the lock members but to prohibit the headrest stays from moving downwards.
FIG. 9 is a partially broken exploded perspective view of an example thereof. FIG. 10 is a cross-sectional perspective view of a main part according to the example. A headrest stay 3 of a headrest is inserted and supported in a tubular headrest bush 6, and a height adjusting mechanism 7 is attached to the headrest bush 6 at a position corresponding to an upper end portion of a seat back. In the height adjusting mechanism 7, a lock plate (lock member) 8 is attached to the headrest bush 6 so as to be free to reciprocate perpendicularly to the headrest stay 3, which penetrates the lock plate 8. A portion 8a of the lock plate 8 is pressed against the penetrating headrest stay 3 due to a resilient force of a spring 12. In practice, the lock plate 8 and the spring 12 are accommodated in a case 13, and only an operating portion 8b of the lock plate 8 protrudes outside. The headrest stay 3 has a plurality of height adjusting notches 4 that are arranged at a predetermined spacings. The lock plate 8 engages one of the notches 4 due to the resilient force of a spring 12, whereby the headrest stay 3 is locked. As shown in FIGS. 9 and 10, each of the height adjusting notches 4 is formed of a horizontal face 4a that extends toward the center of the headrest stay 3 and an inclined face 4b that extends downwards from the deepest portion of the horizontal face 4a while gradually increasing in distance from the center of the headrest stay 3.
In this construction, when the headrest is pulled (drawn out) upwards, the portion 8a of the lock plate 8 abutting on the headrest stay 3 is released from the notch 4 against the resilient force (spring force) of the spring 12 owing to an operation of the inclined face 4b of the notch 4. As a result, the headrest stay 3 can move upwards and the height of the headrest can be adjusted. On the contrary, when the headrest is pressed downwards, the lock plate 8 remains engaged with the horizontal face 4a of the notch 4 without being released therefrom. Therefore, the headrest stay 3 is allowed to move downwards by pressing the operating portion 8b of the lock plate 8 against the spring 12 and releasing the lock plate 8 from the notch 4. Consequently, the downward movement of the headrest can be adjusted.
As is apparent from the foregoing construction, the headrest equipped with the conventional height adjusting mechanism as described above can be easily drawn out from the seat. Therefore, the headrest may be drawn out inadvertently or on purpose, which raises a problem in that the safety of a passenger cannot be guaranteed in case of an accident such as a collision.
Thus, a headrest provided with a headrest removal prevention mechanism is disclosed as a solution to the problem (e.g., see JP-2003-259935 A).
The conventional headrest removal prevention mechanism can prevent the headrest from falling off. However, there is a problem in that the headrest cannot be drawn out from the seat. In practice, however, it is often necessary to draw the headrest out from the seat for cleaning, maintenance, and the like.